In a mixing bowl, combine the diced tomatoes, red onion, basil, balsamic vinegar, olive oil, garlic, salt, and black pepper. Stir well and let it sit for about 10 minutes to allow the flavors to meld.
In another bowl, beat the softened cream cheese until smooth. Add the mozzarella cheese, Parmesan cheese, and Italian seasoning, mixing until well combined.
Preheat your oven to 375°F.
Spread the cream cheese mixture evenly in a baking dish. Top with the tomato mixture, spreading it out evenly over the cream cheese layer.
Bake in the preheated oven for 20-25 minutes, or until the dip is bubbly and golden on top.
While the dip is baking, arrange the baguette slices on a baking sheet and toast in the oven for about 5-7 minutes, or until lightly golden.
Remove the dip from the oven and let it cool for a few minutes before serving. Serve warm with the toasted baguette slices.